In a process for manufacturing semiconductor integrated circuits or the like, a film forming apparatus has been used. In this film forming apparatus, for example, a sample holder is used as a component which holds each sample, such as a semiconductor wafer. As the sample holder, for example, an electrostatic chuck disclosed in Japanese Unexamined Patent Application Publication No. 7-130826 (hereinafter referred to as “Patent Document 1”) may be mentioned. The electrostatic chuck disclosed in Patent Document 1 includes a ceramic substrate and an electrode provided therein. This electrostatic chuck mounts an object to be heated on a main surface of the ceramic substrate.
However, in the electrostatic chuck disclosed in Patent Document 1, when a high frequency alternating current is allowed to pass through the electrode, since the electrode generates heat, molecules in the ceramic substrate may react with oxygen contained therein in some cases. Accordingly, the dielectric tangent may be partially increased in the ceramic substrate. As a result, the thermal uniformity of the main surface of the ceramic substrate may be degraded in some cases.